Fix REFRESH MATERIALIZED VIEW to report activity to the stats collector.

Fix REFRESH MATERIALIZED VIEW to report activity to the stats collector.

The non-concurrent code path for REFRESH MATERIALIZED VIEW failed to
report its updates to the stats collector.  This is bad since it means
auto-analyze doesn't know there's any work to be done.  Adjust it to
report the refresh as a table truncate followed by insertion of an
appropriate number of rows.

Since a matview could contain more than INT_MAX rows, change the
signature of pgstat_count_heap_insert() to accept an int64 rowcount.
(The accumulator it's adding into is already int64, but existing
callers could not insert more than a small number of rows at once,
so the argument had been declared just "int n".)

This is surely a bug fix, but changing pgstat_count_heap_insert()'s API
seems too risky for the back branches.  Given the lack of previous
complaints, I'm not sure it's a big enough problem to justify a kluge
solution that would avoid that.  So, no back-patch, at least for now.

Jim Mlodgenski, adjusted a bit by me

Discussion: https://postgr.es/m/CAB_5SRchSz7-WmdO5szdiknG8Oj_GGqJytrk1KRd11yhcMs1KQ@mail.gmail.com